A restraint device including a catch defining a space for receiving a wire and a movable member mounted for movement between a first position, in which the member is spaced from the catch, such that a wire is able to be inserted sideways into the space, and a second position, in which the movable member prevents the wire from being inserted sideways into the space. A biasing device resiliently urges the movable member toward the second position, such that the movable member clamps the wire against the catch. The restraint device is mounted on the casing of a computer or the like, or on a mounting member securable in or across an opening in the casing. One or more of the restraint devices can be mounted on a mounting member.